(1) Field of the Invention
The present invention relates to an internal combustion engine equipped with an electronic controlled throttle system for operating a throttle valve equipped in an intake system of the engine to be opened and closed by an actuator to a target position, and more specifically, to a fail-safe control technique in an engine comprising two accelerator position sensors and two throttle position sensors or comprising at least two throttle position sensors, wherein said fail-safe control is performed in case one sensor out of said two sensors fails to operate.
(2) Related Art of the Invention
Conventionally, an electronic controlled throttle system is known where the opening (position) of the throttle valve is electronically controlled based on the accelerator position (step-in quantity of the accelerator pedal) and the engine rotation speed and the like, so as to gain a target air quantity (Japanese Unexamined Patent Publication No. 7-180570).
Of such known electronic controlled throttle systems, the ones that are not equipped with a limp-home structure for mechanically linking the throttle valve by means of the accelerator operation through a wire and the like (full electronic controlled throttle system) are applied, for example, with the following system in case the drive system fails to operate. The system includes two accelerator position sensors and two throttle position sensors, and as for the accelerator position or opening, the smaller value of the two detection values is selected (so as to prevent excessive output), and as for the throttle valve position or opening, the value detected by the main throttle position sensor is used, wherein in some cases, the greater value of the two detection values is selected (the greater value is selected and the value is corrected to a smaller value by a feedback control, thereby preventing excessive output).
According to the fail-safe method in such full electronic controlled throttle system, when one of the two sensors fails to operate (hereinafter called single failure) and the control is switched to utilize only the value detected by the remaining working single sensor, the promptness of failure detection provided by equipping double sensors is lost. Therefore, when the remaining working sensor also breaks down, the change in engine output will become large for a period of time until the failure is judged to have occurred. For safety, such trouble must be prevented.
The present invention is aimed at solving such problem of the conventional system mentioned above. The object of the present invention is to enable the vehicle to travel at the minimum speed necessary (limp-home) while preventing the excessive increase of the engine output, when single failure occurs to either of the two accelerator position sensors or the two throttle position sensors.
Further object of the present invention is to prevent the excessive increase of the engine output by limiting either the absolute value and/or the increase rate of the output.
Another object of the present invention is to enable the vehicle to travel at a speed corresponding to need while preventing the excessive increase of the engine output, when single failure occurs to one of the two throttle position sensors.
Another object of the present invention is to prevent the excessive increase of the engine output more securely during single failure of the throttle position sensor.
Further object of the present invention is to prevent the stalling of the vehicle caused by unnecessary decrease of the engine output during single failure of the throttle position sensor.